Solvent extraction processes using application of an electric field to enhance mass transfer from one phase into the other are commonly known as “electroextraction”. When an electrical field is applied in a two-phase liquid—liquid system consisting of a low conductive organic phase and a highly conductive aqueous phase, charged compounds that are in the organic phase will migrate fast toward the aqueous phase. As the aqueous phase is entered, migration speed decreases dramatically, causing analyte concentration at the interface.
Originally, electroextraction had been developed as a purification technique in the field of chemical engineering to enhance product yields, see for instance U.S. Pat. No. 3,841,984 and U.S. Pat. No. 3,472,080. More recently, electroextraction has been adapted for analytical purposes, extracting compounds from an organic into an aqueous phase in capillary vessels, as disclosed for instance in J. Chromatogr. A 1994, 687, 333-341 and Electrophoresis 2010, 31, 3903-3912. While this generally is a very effective process, it requires the analytes to be dissolved in an organic phase, which limits the potential application to molecules having an appropriate solubility, and involves an extra diluting step in the analytical procedure, i.e. the mixing of the sample with an organic phase.
A different approach was disclosed in WO-A-2007004892. Herein a process is disclosed for the electro-assisted extraction of at least one ionized or partially ionized organic compound from a first hydrophilic donor solution through a liquid membrane comprising an immobilized organic solvent into a second hydrophilic acceptor solution. While this process may allow extracting aqueous analyte samples from a first into a second aqueous solution, the presence of the membrane will only allow a limited number of compounds to pass into the receptor solution due to the transport limitation associated with the liquid membrane, and the fact that the artificial liquid membrane discriminates the majority of endogenous compounds from a biological matrix, which is highly undesired in metabolomics. Yet further, the device is complex, and the membrane will need to be discarded after a single application. Accordingly, there remains a need to improve the efficiency of the electroextraction processes.